HCS101
DS41115D-page 6 Preliminary 1999-2013 Microchip Technology Inc.
4.3.4 MINIMUM FOUR TRANSMISSIONS
(MTX4)
If this bit is cleared, at least one code word is completed
when the HCS101 is activated. If this bit is set, at least
four complete code words are transmitted.
4.3.5 TRANSMIT PULSE ENABLE (TXEN)
If this bit is cleared, no start pulse occurs before a
transmission. If the bit is set, a start pulse (1 T
E long) is
transmitted before the first code word’s preamble.
4.3.6 S3 SETTING (S3SET)
This bit determines the value of S3 in the function code
during a transmission and the high trip point selected
by VLOWS in Section 4.3.2. If this bit is cleared, S3 mir-
rors S2 during a transmission. If the S3SET bit is set,
S3 in the function code is always set, independent of
the value of S2.
4.3.7 EXTENDED SERIAL NUMBER
(XSER)
If this bit is cleared, the most significant four bits of the
32-bit Serial Number 1 are replaced with the function
code. If this bit is set, the full 32-bit Serial Number 1 is
transmitted.
5.0 SPECIAL FEATURES
5.1 Code Word Completion
Code word completion is an automatic feature that
ensures the entire code word is transmitted, even if the
button is released before the transmission is complete.
If the button is held down beyond the time for one code
word, multiple code words will result. If another button
is activated during a transmission, the active transmis-
sion will be aborted and a new transmission will begin
using the new button information.
5.2 Blank Alternate Code Word
Federal Communications Commission (FCC) Rules,
Part 15 specify the limits on fundamental power and har-
monics that can be transmitted. Power is calculated on
the worst case average power transmitted in a 100 ms
window. It is therefore advantageous to minimize the
duty cycle of the transmission by minimizing the duty
cycle of the individual bits and by blanking out consecu-
tive words. The transmission duty cycle can be lowered
by setting BRS. This reduces the average power trans-
mitted and hence, assists in FCC approval of a transmit-
ter device. Shortening the code word length and
transmitting only every other code word (Figure 5-1) also
may allow a higher amplitude transmission for greater
range.
5.3 Auto-Shutoff
The auto-shutoff function automatically stops the
device from transmitting if a button inadvertently gets
pressed for longer than the time-out period, T
TO. This
will prevent the device from draining the battery if a but-
ton gets pressed while the transmitter is in a pocket or
purse.
5.4 VLOW: Voltage LOW Indicator
The VLOW bit is included in every transmission and will
be transmitted as a one if the operating voltage has
dropped below the low voltage trip point. Refer to
Figure 3-2. The trip point is selectable based on the
battery voltage being used. See Section 4.3.2 for a
description of how the low voltage select option is set.
FIGURE 5-1: CODE WORD TRANSMISSIONS
One Code Word
BRS = 0
BRS = 1
A
2A
100ms 100ms 100ms 100ms
Amplitude
Time
